Validity and reliability of the Korean caregiver contribution to self-care chronic illness inventory

The contribution of caregivers to self-care for chronically ill patients is important for improving patient outcomes. The Caregiver Contribution to Self-Care Chronic Illness Inventory (CC-SC-CII) has been used to assess caregivers’ contributions to three distinct aspects of self-care (maintenance, monitoring, and management) globally. This study aimed to examine the psychometrics of the Korean version of the CC-SC-CII with 230 family caregivers (mean age = 49.8 years, 70% women) of patients with chronic illness. We demonstrated that the CC-SC-CII-Korean has good reliability with acceptable internal consistency and construct validity for all three factors using confirmatory factor analysis. The CC-SC-CII-Korean is a reliable and valid instrument to measure the contributions of Korean caregivers to the self-care of patients with chronic illnesses.

Item analysis. A 19-item CC-SC-CII instrument specifically measures caregivers' contributions to self-care maintenance, monitoring, and management of patients with chronic illness 23 . The average score for each item ranged from 2.92 to 4.40 points, with a maximum score of 5. Skewness ranged from − 1.66 to − 0.29, and kurtosis ranged from − 0.67 to 2.17, indicating that all items had a normal distribution. The corrected item / total correlation coefficient between individual items and all items was 0.30 or higher, confirming the internal consistency of the items ( Table 2)    Squared multiple correlations ranged from 0.44 to 0.84, and the standardized factor loadings ranged from 0.51 to 0.71. The results of CFA in the self-care maintenance model supports that each set of items represents a single subjacent construct (Fig. 1).
Caregiver contribution to self-care monitoring. In this study, the caregiver contribution to self-care monitoring was assumed to be the same dimension as in the original scale-that is, self-care monitoring behaviors. The analysis suggested a suitable model with a single-factor solution, as in the original scale. The five self-care monitoring items showed suitable threshold levels (χ 2 = 90.35, df = 14, P < 0.001), and a reasonable fit of the model index to the data (CFI = 0.99, TLI = 0.99, GFI = 0.99, AGFI = 0.91, RMSEA = 0.03, NFI = 0.97, and IFI = 0.99).  Caregiver contribution to self-care management. The caregiver contribution to self-care management was assumed to have two secondary factors: autonomous behaviors and consulting behaviors. However, the results of the CFA did not fit this assumption well since the RMSEA was high (χ 2 = 99.03, P = 0.04, df = 53; CFI = 0.87, TLI = 0.83, GFI = 0.85, AGFI = 0.81, RMSEA = 0.10, NFI = 0.81, and IFI = 0.84). Instead, the analysis indicated a more suitable model with a single-factor solution. The seven items for the caregiver contribution to self-care management showed suitable threshold levels (χ 2 = 108.80, P < 0.001, df = 51), and a reasonable fit of the model index to the data (CFI = 0.91, TLI = 0.93, GFI = 0.91, AGFI = 0.86, RMSEA = 0.07, NFI = 0.90, and IFI = 0.91).
The squared multiple correlations ranged from 0.59 to 0.85, and the standardized factor loading ranged from 0.50 to 0.89. The CFA of the self-care management model also supports offers evidence of an acceptable fit (Fig. 3).
Simultaneous confirmatory factor analysis of the CC-SC-CII-Korean. Figure 4 presents confirmatory factor analysis results to verify a general model with all items and a three-factor structure of the CC-CS-CII-Korean.
In the fit test for the 19-item CC-CS-CII-K model consisting of three factors, all fitness indices met the criteria (χ 2 = 310.85 [P < 0.001], df = 149, CFI = 0.91, TLI = 0.91, NC = 2.09, RMSEA = 0.07, AGFI = 0.90, NFI = 0.8) 33 . The CFA showed that all factor loadings were significant, from 0.59 to 0.87 (Fig. 4). These results establish that the factors essential to the scales emerged plainly, even when the analysis was done on a mixture of items and factors. Table 3 shows the test results of the construct validity of the CC-SC-CII-Korean items adopted through confirmatory factor analysis. In this study, construct validity of the items was confirmed based on three criteria. First, the standardized estimate (β) value was found to be 0.50-0.86, satisfying the standard criterion of 0.50 or more. Second, average variance extracted (AVE) the value obtained by dividing the sum of the provided values of the standardized load by the sum of the square of the standardized factor load and the sum of the study error variance was 0.54-0.72, which also satisfied the standard criterion of more than 0.50. Third, construct reliability (CR) the value obtained by dividing the square of the sum of the standardized factor loads by the square of the sum of the standardized factor loads and the sum of the study error variance was found to be above the standard value of 0.70 (range, 0.82-0.93) ( Table 3), thus confirming the construct validity of the instrument by satisfying all three conditions.
The construct validity of the CC-SC-CII-Korean was also supported by the convergent validity. With reference to the Caregiver Self-Efficacy in Contributing to Patients Self-Care (CSE-CSC) scale 34 , the Pearson correlation coefficients for each of the three factors-caregiver contributions to self-care maintenance (r = 0.52, P < 0.001), caregiver contributions to monitoring (r = 0.55, P < 0.001), and caregiver contributions to management (r = 0.68, P < 0.001)-demonstrated the construct validity.
Internal consistency reliability. An analysis of the internal consistency reliability and score distribution for the 19 items of CC-SC-CII-Korean, showed a Cronbach's α value of 0.75 for the seven items of the maintenance, 0.90 for the five items of the monitoring scale, and 0.81 for the seven items of the management scale (Table 3) 35 .

Discussion
This study verified the validity and reliability of the CC-SC-CII-Korean which was developed to measure the contributions of caregivers to self-care for chronically ill patients. Participants in this study differed from participants of the previous study in that parents of patients with chronic diseases are included. The average age of the patients in this study was 63.22 years (ranging from 18 to 82 years), and compared to the participants in the previous study (average age 76.6, ranging from 65 to 93 years), younger patients were included 23 . Nevertheless, the CC-SC-CII-Korean showed good validity and reliability among Korean caregivers for patients with chronic diseases. In the case of patients diagnosed with chronic diseases in childhood and adolescence, they perform self-care activities for the disease with support from their parents until young adults 36 . In other words, parents play an important role in caring for children with chronic diseases to adapt to the disease and maintain self-care behavior [36][37][38] . The results of this study confirmed the caregiver's contribution scale to the self-care behavior of chronic diseases applies not only to middle-aged and old patients but also to young adult patients. However, it needs to be further validated in a larger sample and wider age range of care recipients in the future.
Securing equivalence with the original instrument is important in instrument translation for cross-cultural healthcare studies. The translation/back-translation process alone cannot guarantee translation equality 28,39 . A committee went through the translation verification process for instructions, items, and response formats of the reverse translation instrument to increase the validity of the evaluation scale. The role of committee members was = Factor correlation; = Factor; = Factor loading; = Items; = Error variance; Item 1 = enough sleep; Item 2 = avoid getting sick; Item 3 = physical activity; Item 4 = eat special foods or avoid certain foods; Item 5 = keep appointment for health care; Item 6 = take prescribed medicines; Item 8 = smokingcessation; Item 9 = monitor the health condition; Item 10 = monitor for medication side-effects; Item 11 = monitor to changes in how one feels; Item 12 = monitor one tires more than usual; Item 13 = monitor for symptoms; Item 14 = recognize it as a symptom; Item 15 = care for eats or drinks; Item 16 = care for to change the activity level; Item 17 = care for to take a medicine; Item 18 = talk about the symptom to the healthcare; Item 19 = ask the healthcare provider for guidance; Item 20 = make him/her feel better. www.nature.com/scientificreports/ to review translation inconsistencies, inappropriate expressions, and concepts that may arise during the research process and revise each phrase as required to fit the target culture and sentiment 28 . As a result, two items were modified to more familiar expressions among similar words to suit the Korean culture and healthcare environment. This was also implemented in previous studies that evaluated the understandability of the original text and addressed any inaccuracies or ambiguities in the content of the translated scale relative to the original text 24 .
The CFA was used for the validation of structural feasibility in construct validity. Results showed that the CC-SC-CII-Korean had three valid factors.
The original self-care maintenance factor included two dimensions: health-promoting behaviors (items 1, 3, 8) and illness-related behaviors (items 2, 4, 5, 6). On the CC-SC-CII-Korean, however, self-care maintenance (items 1, 2, 3, 4, 5, 6, 8) was identified as a single dimension. This result differs from the results of a previous study conducted in China 24 . This finding may be a cultural phenomenon that reflects Korean treatment standards.
In Korean caregivers, getting enough sleep, being physically active, managing stress, and eating healthy foods tailored to the disease are considered health-related behaviors for self-care maintenance. In other words, healthpromoting behaviors and illness-related behaviors are considered the same concept rather than strictly separated. Health-promoting behaviors directly related to diseases such as Items #5 and #6 (taking prescribed medications, keeping appointments) fall under illness-related behaviors and may seem not essential for health-promoting behaviors, but in this study, all of them were the same. This is similar to the results of a study that found that chronically ill patients recognize regular physical activity, healthy eating habits, regular medical care, and compliance with prescription drug intstructions as self-care behaviors 40,41 . In addition, lack of sleep can have adverse health effects on patients with chronic diseases, so 'sufficient sleep' is not only a health-promoting behavior, but also an illness-related behavior 42 .This is similar to improved disease-related clinical outcomes (blood pressure, cholesterol levels, etc.) in which stroke survivors conducted illness-related health promotion activities such as daily physical activity, proper sleep time, stress management, and cholesterol-controlled food 43 . More research is needed to achieve a deeper understanding of the implications of this result.
On the CC-SC-CII-Korean, the monitoring factor (items 9, 10, 11, 12, 13) was found to be the same as the original instrument. These items were for monitoring the patients' condition, treatment-related side effects, normal activities, and symptoms, as well as attention to mood changes in patients. The self-care monitoring of chronically ill patients involves not only systematic and continuous monitoring of the body, but also careful monitoring of psychological changes 7,12 . In Korean culture, patients rely on healthcare professionals' direction, so a difference between maintenance and monitoring is expected. Caregivers are taught by healthcare professionals to monitor the patient's health status, including weight, blood sugar, blood pressure, temperature, medication side effects, emotional changes, disease-related symptoms and disease-related health behaviors 44 .These results might reflect the benefits of education specifically on disease-related monitoring items for chronic disease patients and their family caregivers.
On the CC-SC-CII-Korean, management factor (items 14,15,16,17,18,19,20)-was found through CFA. The original instrument included two dimensions: autonomous behavior (items 14,15,16,17,20) and consulting behavior (items 18,19). Autonomous behavior refers to behaviors that an individual chooses autonomously based www.nature.com/scientificreports/ on previous experiences when experiencing any symptoms. Consulting behavior represent behaviors that are encouraged by someone other than oneself, such as healthcare professionals 23 . This is somewhat different result from previous studies 23,24 . Our interpretation of the results of the one-dimensional model of this study sample is that in Korean healthcare culture, caregivers often consult and listen to advice from healthcare professionals. In addition, caregivers receive education in advance on necessary self-care actions, such as taking medications or changing diet and lifestyle, when a patient's symptoms change 43,45 . As a result, autonomous behavior and consulting behavior are closely related. However, these results are from a sample in our study and further research is needed to confirm this factor structure. This instrument demonstrated construct validity, and we found significant and strong correlations between caregivers' self-efficacy and three caregivers' contributions to self-care. Our finding was supported by relevant theory 7 , and the results were similar to the previous studies 23,24 . We demonstrated that the CC-SC-CII-Korean was a reliable instrument with adequate internal consistency.
The core of this research was the translation and validation of instruments that have not hitherto been available for use with informal caregivers who support patients with self-management of chronic conditions. The CC-SC-CII-Korean provides a comprehensive assessment of the caregiver's contribution to self-care maintenance, monitoring, and management and helps caregivers detect potential gaps in these three areas. The CC-SC-CII-Korean could also assist health care providers and researchers in planning and implementing interventions for caregivers to improve self-care support for people with chronic conditions. Self-care for chronic disease patients is a continuous process, and this instrument can both objectively monitor the caregiver's contribution to the patient's self-care and serve as a motivator for positive change.
The CC-SC-CII-Korean scale, which validity and reliability have been verified in this study, is expected to be useful in measuring the contribution of caregivers to self-care in chronic disease patients. However, this study has several limitations. First, the subjects of this study were recruited through convenience sampling among the family caregivers of chronic disease patients visiting university hospitals in Seoul and Yongin, which are relatively large cities in Korea. Therefore, caution is required when generalizing the results of this study, and in the future, repeated studies targeting family caregivers of chronic disease patients in various communities are required. Second, although the caregivers participating in this study included the possible range of family caregivers in Korean culture, it was not possible to identify differences in the contribution of caregivers to each patient's self-care according to caregiver's characteristics. However, previous studies conducted in other cultures have suggested that caregivers may differ depending on age, population, patient comorbidity, and culture, and in the future, dyadic research can be conducted among patients and family care providers to investigate their interactions and the effects of managing the chronic disease 23,24 . In addition, the amount of self-care required varies according to the number of chronic diseases, specific diseases, and severity [46][47][48] , therefore, future studies should analyze various diseases characteristics. Third, while the caregivers in our sample consisted of family members, further studies with informal caregivers who had various relationships with patients, including friends, neighbors, and colleagues, are needed.
In conclusion, this study shows that the CC-SC-CII-Korean has good validity and reliability and can be used in clinical and research studies to evaluate the contributions of caregivers to self-care for chronically ill patients in Korea. This instrument can measure the contribution of caregivers to patients' self-care, which is significant given the annually increasing rate of chronic disease in Korea. This instrument also allows healthcare professionals to understand how well a caregiver contributes to better patient outcomes.

Methods
Research design and participants. This cross-sectional study was performed at chronic illness clinics in two university hospitals in South Korea. Between the two sites, a convenience sample of 230 adult caregivers of patients with chronic illness was enrolled. Considering that the sample size required to test psychometric properties of the instruments must be at least 10 times the number of items, which was 19 35 , at least 190 participants were required. Based on the literature, 230 people were targeted, considering a dropout rate of 10% for the questionnaire and a dropout rate of 5% due to insincere responses 35 . Therefore, as 230 people participated, the instrument was considered verified. The eligible criteria of informal caregivers were ≥ 18 years old, identified by the patient as the main informal caregiver (family or otherwise), and provided most informal care to the patient, able to read and write in Korean. Those with severe illiteracy (i.e., an inability to fully respond to the research questionnaire) were excluded.
All study participants gave written informed consent and were told of their right to withdrawthe study at any time. The study followed the principles delineated in the Declaration of Helsinki, was conducted with the approval of the Ethics Committee of Severance Hospital, and was performed according to the STROBE section guidelines.

Instrument. Caregiver contribution self-care of chronic illness inventory (CC-SC-CII)
. The Caregiver Contribution to Self-care of Chronic Illness Inventory (CC-SC-CII) is a 19-item instrument that acts as a caregiver version of the SC-CII. It specifically measures the contributions of caregivers to self-care maintenance, monitoring, and management of patients with chronic illness 23 . The maintenance subscale (7 items) measures the contributions of caregivers to the patient to do behaviors to maintain of health; the monitoring subscale (5 items) evaluates the behaviors that the caregivers contribute for patients monitoring signs and symptoms of condition; the management subscale (7 items) measures the contributions of caregivers to the patient managing the signs and symptoms of the condition. The CC-SC-CII asks caregivers to report their involvement in the self-care of patients. In instruments, a 5-point Likert scale is used for answers (from 1 "never" to 5 "always"). It uses a standardized score from 0 to 100, with higher scores reflecting greater caregiver contributions to self-care and 70 used as the threshold for appropriateness. The original psychometric properties of the CC-SC-CII support both  23 . The CC-SC-CII is an instrument whose original and Chinese versions have been verified to have compositional validity in three factors: caregiver contribution to self-care maintenance, caregiver contribution to self-care monitoring, and caregiver contribution to self-care management 24 .
Study procedure. Translation/back-translation0. After receiving permission from the original author 23 , the CC-SC-CII was translated into Korean, following guidelines for transcultural adaptation 28 . The CC-SC-CII was translated into Korean by two independent Korean researchers who were fluent in English and had expertise in chronic illness. The Korean version of the CC-SC-CII was then translated back to English by a bilingual researcher. A committee was constituted of experts involved in research or work teams associated with chronic illness to ensure no loss of meaning appeared during the translation process and to establish parity with the original instrument. Seven experts were selected: two clinical nurses in chronic illness practice; two chronic illness research nurses, two professors from a college of nursing in Korea, and one professor from a college of nursing in the US. After that, cognitive interviews using think-aloud techniques were conducted with the two chronic illness clinical nurses to verify that all items of the CC-SC-CII were easily and correctly understood.

Content validity verification.
For the content validity of the CC-SC-CII-Korean instrument, two experts in the management of chronic illness patients, one nursing professor and one clinical practitioner, were chosen by the professional evaluation team to calculate suitability using item-content validity index (I-CVI) values, with 1 point for "not very suitable, " 2 points for "not suitable, " 3 points for "fit, " and 4 points for "very suitable 32 . " The selected items had 3 or 4 points 100% of the time 32 .
Data collection. Data were collected between October 2021 and February 2022. When trained research assistants met with potentially eligible participants, they confirmed eligibility of caregivers and then elucidated the study purpose. After eligible caregivers who were interested in the study signed an informed consent form, they were asked to fill out questionnaires, including socioeconomic and clinical characteristics, CC-SC-CII-Korean, and Caregiver Self-Efficacy in Contributing to Patient Self-Care (CSE-CSC) scale 34 on paper or online.
We added the ten-item CSE-CSC scale-derived from the Self-Care Self-Efficacy Scale (SC-SES)-to test a construct validity by hypothesizing that higher scores of the CC-SC-CII are associated with better caregiver efficacy in contributing to patient self-care 12 . The CSE-CSC measures caregiver efficacy in contributing to selfcare maintenance, monitoring, and management for patients with chronic illness 34 . The CSE-CSC scale uses a 5-point Likert format, with responses from "not confident" to "very confident. " The CSE-CSC scores correspond to greater caregiver efficacy in contributing to self-care for patients with chronic illness 34 .
Data analysis. The data were analyzed using SPSS version 25.0 and AMOS version 26.0 (IBM Corp. Armonk, NY, USA). The sociodemographic characteristics of participants were calculated as frequency, percentage, mean and standard deviation, and the normal distribution and internal consistency of the items were confirmed through item analysis of the instrument. The content validity test of the instrument was evaluated using a 4-point Likert scale from the expert group and calculated using the I-CVI.
The CC-SC-CII was developed according to the middle-range theory of self-care of chronic illnessand determined the three dimensions of the scale 23 . Confirmatory factor analysis was conducted to verify the construct validity, and the suitability of the model was evaluated by the absolute fit index, relative fit index, and parsimonious fit index. The absolute fitness index is an evaluation of the degree to which the collected data and the research model match for the suitability analysis of the question composition, and was adjusted by the 22 statistic (freedom, p-value), the normal chi-square (NC), and the approximate error average square (root mean error of application) (Adjust) (FIexA). The relative fitness index represents how accurately the researcher's structural equation model was measured by comparing it with a model without correlations between variables (Young model), and fit was confirmed by the standard fit index (NFI) and the comparative fit index (CFI). Regarding the criteria for each index to be evaluated as suitable, the smaller the 22 statistic, the larger the p-value, and if it is greater than 0.05, it is generally accepted that the suitability is high. However, the 22 statistic is sensitive to the number of samples, and as the size of the sample increases, the 22 statistic increases; thus, even if it is statistically significant, the suitability is not necessarily low. As an indicator used to compensate for this, it is considered appropriate if the NC, obtained by dividing the 22 statistic by the degrees of freedom, is 3.0 or less. RMSEA is very good if it is less than 0.05 and appropriate if it is in the range of 0.05-0.08. AGFI, NFI, and CFI are evaluated to be very good for values of 0.90 or higher, and can be evaluated as suitable in the range of 0.70-0.90. In addition, significance (critical ratio [C.R.]) confirmed the relationship between latent factors and constituent variables 49 . In order to secure the construct validity of the items, it is desirable that the standardized factor load (β) reach a minimum standard of 0.50 or more, the reliability of concept (CR) should be 0.70 or more and 0.95 or less, and the mean variance extraction index (AVE) should be 0.50 or more 33,49 .
The correlation between the CC-SC-CII score and the CSE-SSC scale score was investigated using Pearson correlation coefficients (r). Each caregiver's contribution to patients' self-care was expected to positively correlate to the theory and results of previous studies 7, 12 .
Lastly, the reliability of the instrument was confirmed by item-total correlation and internal consistency between items using Cronbach's α values. When Cronbach's α value is between 0.70 and 0.80, the internal consistency reliability is good, and when it is 0.80 and 0.90, it is very high 35 .